8 – Corynebacterium, Rhodococcus Flashcards
Microbiology Characteristics
- Biocontainment level 2
- Aerobic and facultative anaerobes
Corynebacterium characteristics
- Gram-positive clubbed rods
- Characteristic ‘palisades’ or ‘Chinese letter’
- Colony morphology is variable
Rhodococcus characteristics
- Gram-positive cocco-bacilli (‘egg shaped’)
Rhodococcus equi on blood agare
- Produces pink colonies
o Pigment can be enhanced on other differential media - Facultative intracellular parasite
Natural Host or Habitat
- Part of normal microbiota (skin, mucous membranes, intestinal tract)
- Can survive in environment
Corynebacterium pseudotuberculosis
- Survive in environment for up to 55 days
Rhodococcus equi
- Soil organism
o Feces contaminated soil
Taxonomy
- Oxidative (Rhodococcus) or fermentative (Corynebacterium)
Virulence Factors: C. renale, cystidis, pilosum
- Pilli: attachment
- Urease: production of ammonia
Virulence factors: C. pseudotuberculosis
- Phospholipase D
o Essential VF
o Damage host cell membranes=facilitates spread
o Cytotoxic: erythrocytes, neutrophils
Virulence factors: R. equi
- Virulence associated proteins (VAPs)
o Allows organism to survive intracellularly (prevents acidification of phagosome)
Virulence factors: C. diphtheriae: canonical toxigenic infection (model)
- One of the most studied toxins
- Diphtheria toxin acts by interfering with host cell protein synthesis
Clinical significance: C. pseudotuberculosis (sheep, goats)
- Causes of caseous lymphadentis
- Pyogranulomatous abscesses of lymph nodes and organs
o Contain inspissated material (caseous) - Highly contagious
- Difficult to eradicate once herd infected
- Antimicrobials don’t penetrate into lesions
- Worldwide distribution
Clinical significance: C. renale group (bovine)
- Infections of bovine urinary tract (C. renale, cystitidis, pilosum)
- Cystitis
- Pyelonephritis
- *maintained in herd by subclinical carriers and diseased animals
Clinical significance: C. renale group (bovine), cystitis
- Infection of urinary bladder
- Generally, not systematically sick
- Hematuria
- Proteinuria
Clinical significance: C. renale group (bovine), pyelonephritis
- Infection of kidney
- Fever
- Depression
- Reduced feed intake
Clinical significance: C. renale group (bovine), subclinical carriers and diseased animals
- Transmission by urine droplets splashing from infected onto vulva of susceptible cow
- *isolate affected animals=difficult to eradicate from infected herds
Clinical significance: C. renale group (bovine), attachment facilitated by alkaline conditions, inhibited by acid
- Urease producing organism: converts urea into ammonia
- Urinary acidification may be helpful
Clinical significance: C. renale group (bovine), treatment
- Penicillin
Clinical significance: C. renale group (bovine), likelihood of treatment success decreases as disease progresses
- More difficult to eradicate from kidney
- Prognosis worsens with increasing renal dmage
- Cull rate=1/3
Clinical significance: C. renale (sheep)
- Balanoposthitis (inflammation of penis and prepuce)
o PIZZLE-ROT
Clinical significance: C. renale (sheep), predisposed by high protein diets->high urea concentration
- Urea converted into ammonia by organism
- Ammonia irritates penis
- Inflammation and ulceration
- Bacteria enter compromised tissues
- Scarring over prepuce prevents penile extrusion and breeding
Clinical significance: C. renale (sheep), treatment
- Combination of antimicrobials (penicillin) and debriding dead tissue and removing excess wool
Clinical significance: corynebacterium (dogs and cats)
- Role of these is unclear
- Skin infections (C. auriscanis and C. ulcerans)
o Frequently polymicrobial infections
o Treatment can be challenging - Rare causes of UTI (C. urealyticum)
Clinical significance: C. diphtheria (humans)
- Uncommon in developed countries
- Respiratory diphtheria is most common
o Diphtheritic pseudo-membrane over pharynx - Disease caused by toxigenic strains
- DPT vaccines
Clinical significance: R. equi (horses)
- Severe bronchopneumonia in young foals
o Chronic suppurative bronchopneumonia - Abscessation in older horses (pyogranulomatous pneumonia)
- Enteric disease: seen in 50% of foals with pneumonia
- Acquired from environment (soils contaminated with horse feces)
Clinical significance: R. equi (horses): enteric disease
- Fecal-oral or swallowing expectorate sputum
o Usually pneumonia first - Multi-focal ulcerative enterocolitis and typhlitis
- Weight loss, diarrhea and colic
Clinical significance: R. equi (horses), ubiquitous on horse farms, so why not more common?
- Not sure
- Maybe less virulent strains?
- Management practices?
Clinical significance: R. equi (horses), horses infected when inhale virulent strains
- Only VapA+ isolates are virulent in horses
- Intermediately virulent isolates producing other Vap proteins have been IDed
o Humans: HIV associated infections
o Not found in horses
Clinical significance: R. equi (horses), prognosis
- Chronic disease: fair
- Acute: poor
Clinical significance: R. equi (horses), treatment
- Antimicrobials is key
- Rifampin+macrolide type drug
- *needs drugs that reach high intracellular concentrations
Clinical significance: R. equi (horses), management
- Little evidence of preventive measures
- Clean up manure, avoid crowding, reduce dust, house foals in well ventilated area
Clinical significance: R. equi (cats)
- Rarely reported, but increasing (immunocompromised)
- Causes cutaneous infections
o Characterized by pyogranulomatous inflammation
o Typically non-painful and non-febrile (no fever) - Abscesses with draining tracts + lesions of parenchymal organs
- Treatment: surgical drainage + antimicrobials
Specimens to collect
- Pus or exudates: C. pseudotruberculosis
- Mid-stream urine: C. renale group
- Trans-tracheal wash: R. equi
Sample handling
- Swabs should be sent with transport media
- Do NOT freeze samples
Laboratory ID: Corynebacterium
- Standard culture methods (blood agar)
- Growth may take up to 48hrs
- Readily IDed biochemically
Laboratory ID: Rhodococcus
- May grow better at low temperatures (30 degrees C)
o Include on history - Partially acid-fast
- Growth may take up to 48hrs
- Readily IDed biochemically
Laboratory ID: C. pseudotuberculosis
- Immunological tests to detect exposure/infection in cases where abscesses are NOT superficial enough to sample OR don’t want to contaminate the environment
Laboratory ID: antimicrobial susceptibility test
- No recognized guidelines
- Interpret with caution
- Consult your lab!
C. pseudotuberculosis: zoonotic
- Abscesses in humans associated with sheep herders
- Risk during sheering or while performing necropsy
C. renale: zoonotic
- low risk to human health
Toxigenic C. ulcerans: zoonotic
- Causes cutaneous diphtheria in people
R. equi: zoonotic
- primarily in immunocompromised patients
C. pseudotuberculosis treatment options
- Intracellular infections: antimicrobial therapy difficult
- Control measures depend on prevalence
C. pseudotuberculosis treatment options: control measures
- Low prevalence: stamp out (Ex. cull)
- High prevalence: minimize disease impact
C. spp. are intrinsically resistant to
- Fosfomycin
Possible relevant for UTI treatment in companion animals
Rhodococcus treatment options
- Think MLSbK + rifampin
- Intrinsic penicillin, ampicillin and cephalosporin resistance
